Valve train of an internal combustion engine comprising a tappet and a tappet pushrod

ABSTRACT

The invention proposes a valve train of an internal combustion engine comprising a tappet ( 7 ) and a tappet pushrod ( 1 ) that is actuated by said tappet ( 7 ), said tappet pushrod ( 1 ) being at least partly hollow and comprising on one end ( 3 ), a first support ( 4 ) for an at least indirectly contacting pressure piston ( 5 ) of a hydraulic lash adjuster ( 6 ) of said tappet ( 7 ) that follows a periodic driving element, typically a cam. A second support ( 9 ) for a follower member ( 2 ), typically a rocker arm, is arranged on a further end ( 8 ) of the tappet pushrod ( 1 ). The first support ( 4 ) comprises a passage ( 10 ) for hydraulic medium that can be routed out of the pressure piston ( 5 ) during operation of the internal combustion engine into an interior ( 11 ) of the tappet pushrod ( 1 ), wherein a pipette means ( 12 ) is installed in the tappet pushrod ( 1 ) for retaining a hydraulic medium column during a standstill of the internal combustion engine. Through the pipette means ( 12 ) of the invention, an additional volume of hydraulic medium is available for a rapid filling of the reservoir enclosed by the pressure piston ( 5 ) with pressure medium after a re-starting of the internal combustion engine, so that a proper lash adjusting operation is guaranteed from the very beginning.

FIELD OF THE INVENTION

The invention concerns a valve train of an internal combustion enginecomprising a tappet and a tappet pushrod that is actuated by saidtappet, said tappet pushrod being at least partly hollow and comprisingon one end, a first support for an at least indirectly contactingpressure piston of a hydraulic lash adjuster of said tappet that followsa periodic driving element, typically a cam, a second support for afollower member, typically a rocker arm, being arranged on a further endof the tappet pushrod, said first support comprising a passage forhydraulic medium that can be routed out of the pressure piston duringoperation of the internal combustion engine into an interior of thetappet pushrod.

BACKGROUND OF THE INVENTION

A valve train of the pre-cited type is disclosed in U.S. Pat. No.6,196,175 B1. The tappet of this valve train is configured as aswitchable roller tappet and is installed in a relatively stronglyrestricted mounting space, so that only an inadequate quantity ofhydraulic medium can be contained in its pressure piston. However, invarious situations such as upon re-firing of the internal combustionengine after a longer standstill, “taxi operation” etc., this hydraulicmedium proves to be insufficient for a proper lash adjusting operationof the lash adjuster. Therefore, a relatively high risk of are-aspiration of air into the high pressure chamber of the lash adjusterexists with all the drawbacks, like rattling noises, wear etc., known inthe technical field.

Moreover, it is usual in OHV trains comprising a roller tappet and atappet pushrod to lubricate further components like rocker arms,cam-contacting surfaces etc. that are situated at a high geodetic level,through a hollow tappet pushrod. This is also disclosed in the pre-citedU.S. Pat. No. 6,196,175, while U.S. Pat. No. 3,908,615 likewisediscloses a hollow tappet pushrod. Further, U.S. Pat. No. 5,351,662shows a tappet configured as a roller tappet in which it can be seenthat, for design reasons, the hydraulic lash adjuster can contain only avery small quantity of hydraulic medium.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a valve train of thepre-cited type in which the aforesaid drawbacks are eliminated.

This and other objects and advantages of the invention will becomeobvious from the following detailed description.

SUMMARY OF THE INVENTION

The invention achieves the above objects by the fact that a pipettemeans is installed in the tappet pushrod for retaining, during astandstill of the internal combustion engine, a hydraulic medium columnwhich, as viewed in gravity direction, is situated under the pipettemeans.

In this way, the initially mentioned drawbacks are effectivelyeliminated. Thus, when the internal combustion engine is switched off,the oil accumulated in the interior of the tappet pushrod is retainedafter the principle of a pipette as an additional reserve. When theinternal combustion engine is started, this hydraulic medium can flowinto the reservoir of the pressure piston.

The corresponding one-way valve body, such as, for example, a ball, aplate, a cone or the like opens immediately upon re-firing of theinternal combustion engine due to the then occurring vibrations. Thus,from the very beginning, an adequate quantity of hydraulic medium isavailable for avoiding the aforesaid rattling noises. Even duringso-called “taxi operation”, i.e. during extreme short-distance driving,it is guaranteed that a sufficient quantity of hydraulic medium alwaysaccumulates in the reservoir, so that a re-aspiration of air is avoided.

According to a further feature of the invention, the second support ofthe tappet pushrod, i.e. the support on the rocker arm side alsocomprises a passage for the hydraulic medium. The pipette means of theinvention is preferably intended to simultaneously act as a choke forlimiting the flow of hydraulic medium to this passage. Thus only adefined small quantity of hydraulic medium flows to the higher-leverlubrication points while a larger part of the hydraulic medium isavailable for lash adjustment.

According to still another feature of the invention, a bushing (solid orthin-walled, for example, of sheet metal) comprising the pipette meanson one of its collars and the choke on its other collar can be installedin the tappet pushrod. It is clear that the bushing may be arranged atany height in the tappet pushrod, preferably, however, it is arranged ata very high geodetic level so that, after the internal combustion engineis shut off, a sufficiently high hydraulic medium column, retained afterthe principle of a pipette, is formed under the bushing.

The through-openings on the second support of the bushing may be formed,for instance, by leaf spring-like tongues or by rib-like circumferentialprojections or the like. It is also conceivable to simply perforate thecollar in this region.

It is further proposed to make the tappet pushrod of at least twoseparate, fabricated sections with a cylindrical part situatedtherebetween in which the pipette means and the choke are configured.This fabricated embodiment has, for example, the advantage that thetappet pushrod as a whole is simpler to integrate in differentsurrounding structures. According to a further feature of the invention,a connection between the fabricated sections is achieved through theaforesaid two-piece cylindrical part whose one end comprises the sealingvalve seat and whose other end comprises the stop for the closing bodywhich is arranged for slight axial displacement between these ends andis configured, for example, as a ball, a double-taper cone, a plate ofthe like.

It is clear that such a fabricated tappet pushrod, i.e. a pushrod madeup of a plurality of inter-inserted sections can also be generally usedeven if it does not comprise the pipette means or the choke of theinvention.

According to a final proposition of the invention, the supports of thetappet pushrod are configured as ball heads. These can be madeseparately, but a one-piece configuration with the tappet pushrod isalso within the scope of the invention. In place of the ball heads,supports of other configurations such as pan-like or cylindrical shapesetc. will also occur to a person skilled in the art.

The invention will now be described more closely with reference to theappended drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a valve train comprising atappet and a tappet pushrod,

FIG. 2 is a view of the tappet pushrod comprising a pipette means and achoke of the invention,

FIG. 3 is another view of the tappet pushrod comprising the pipettemeans and the choke of the invention, and

FIG. 4 is still another view of the tappet pushrod comprising thepipette means and the choke of the invention.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 discloses an OHV train comprising a cam-actuated tappet 7 thatacts at one end on a hollow tappet pushrod 1. At this end, the tappetpushrod 1 comprises a first support 4 that is configured as a ball headand is seated on a pressure piston 5 of a hydraulic lash adjuster 6 ofthe tappet 7. On its other end 8, the tappet pushrod 1 comprises asecond support 9 that is likewise configured as a ball head and acts ona follower member 2 configured as a rocker arm.

As can be seen from the figures, the tappet pushrod 1 has a generallyhollow configuration, so that hydraulic medium can be routed through itsinterior 11 to the follower member 2. The hydraulic medium is routed outof the space enclosed by the pressure piston 5, through a first passage10 in the region of the one end 3 of the tappet pushrod 1, the interior11 of the tappet pushrod 1 and a second passage 13 in the region of theother end 8, to lubrication points on the follower member 2. FIG. 1illustrates schematically, a rising hydraulic medium column as is formedafter starting of the internal combustion engine.

As already described above, when the internal combustion engine isturned off, the hydraulic medium column in the pressure piston 5 sinks,under certain circumstances, below an adequate minimum, so that when theengine is re-fired, not enough hydraulic medium for lash adjustment canbe re-suctioned into a high pressure chamber of the hydraulic lashadjuster 6. In the most unfavorable of cases, a re-aspiration of airthen takes place.

To avoid these serious drawbacks, precisely as can be encountered in thecase of very small hydraulic medium reservoirs in confined mountingspaces, it is proposed to arrange a pipette means 12 in the tappetpushrod 1 to retain the hydraulic medium column during a standstill ofthe internal combustion engine.

As best seen in FIGS. 2-4, a choke 14 is likewise created in the regionof the pipette means 12 to limit the flow of hydraulic medium to thepassage 13 in the second support 9. It is understood that this choke 14may also be configured separately from the pipette means 12.

As shown in FIG. 2, the tappet pushrod 1 is composed of two separate,fabricated sections 25, 26. The section 25 comprises the first support4, while the section 26 comprises the second support 9. A cylindricalpart 27, made up of two parts, extends between the sections 25 and 26and connects them to each other. As can be seen in the upper portion ofFIG. 2, each of the upper and the lower part of the cylindrical part 27possesses a stub-like extension 28, 29 pointing away from each other.The extension 28 is inserted into the section 25 of the tappet pushrod 1while the extension 29 is inserted into the section 26 of the tappetpushrod 1.

A closing body 30, configured in the present embodiment as a ball,extends for slight axial displacement between the two parts of thecylindrical part 27. A sealing valve seat 32 for the closing body 30 isformed on an inner end face 31 of the (lower) extension 28. The pipettemeans 12 is thus created.

A stop 34 comprising a plurality of circumferentially spacedthrough-openings 35 for the hydraulic medium is formed in the region ofan inner end face 33 of the upper part of the two-piece cylindrical part27. This results in the formation of the choke 14 in this region.

During the operation of the internal combustion engine, i.e. underprevailing hydraulic medium pressure, the closing body 30 is pressedagainst the stop 34 of the upper part of the cylindrical part 27, sothat a small quantity of hydraulic medium can flow past this toward thefollower member 2. When the internal combustion engine is shut off, theclosing body 30 drops onto its valve seat on the inner end face 31. Withthis, as already mentioned above, the pipette means 12 becomes effectiveand the hydraulic medium accumulated in the interior 11 of the tappetpushrod 1 is retained and is available for a rapid re-filling of thereservoir in the pressure piston 5 of the lash adjuster 6 when theinternal combustion engine is re-started. The hydraulic medium isreleased when the closing body 30 lifts off its valve seat 32 as aresult of the vibrations that set in as soon as the internal combustionengine is started.

According to FIG. 3, a bushing 15, configured here as a thin-walledsheet metal part 23 extends within the tappet pushrod 1. The bushing 15is fixed in position through its outer peripheral surface 16 in theinterior 11 of the tappet pushrod 1, preferably in an upper regionthereof. The bushing 15 comprises two axially opposing annular collars17, 18. A closing body 19, configured in this embodiment as a ball,extends for slight axial displacement between these annular collars 17,18. A sealing valve seat 20 for the closing body 19 is configured on thelower annular collar 17, so that the pipette means 12 is formed in thisregion. The upper annular collar 18, in contrast, serves as a stop 21for the closing body 19 and comprises in the present embodiment,circumferentially spaced leaf spring-like tongues between which thethrough-openings 22 for the hydraulic medium are formed. The mode offunctioning of the pipette means 12 and the choke 14 of this and of theembodiment shown in FIG. 4, corresponds to the description given inconnection with FIG. 2.

According to FIG. 4, the bushing 15 is made as an extruded part 24, i.e.it has a generally solid configuration. The annular collar 18 of thisbushing 15 facing the second support 9 comprises on an inner surface,rib-like circumferential projections between which the through-openings22 of the choke 14 are formed. FIG. 4 shows the closing body 19 inabutment against its valve seat 20 in the region of the lower annularcollar 17.

1. A valve train of an internal combustion engine comprising a tappetand a tappet pushrod that is actuated by said tappet, said tappetpushrod being at least partly hollow and comprising on one end, a firstsupport for an at least indirectly contacting pressure piston of ahydraulic lash adjuster of said tappet that follows a periodic drivingelement, typically a cam, a second support for a follower member,typically a rocker arm, being arranged on a further end of the tappetpushrod, said first support comprising a passage for hydraulic mediumthat can be routed out of the pressure piston during operation of theinternal combustion engine into an interior of the tappet pushrod,wherein a pipette means is installed in the tappet pushrod forretaining, during a standstill of the internal combustion engine, ahydraulic medium column which, as viewed in gravity direction, issituated under the pipette means.
 2. A tappet pushrod of claim 1,wherein the second support comprises a passage for hydraulic medium tothe follower member and the pipette means is configured at the same timeas a choke for limiting a hydraulic medium flow to the passage of thesecond support, or a choke for limiting a hydraulic medium flow isassociated to the pipette means.
 3. A tappet pushrod of claim 2, whereina bushing is installed in the tappet pushrod, which bushing is one offixed in position in the interior of the tappet pushrod or is a part ofthe tappet pushrod and comprises two axially opposing annular collarsbetween which a closing body, typically a ball, extends for slightdisplacement, a sealing valve seat for the closing body for forming thepipette means is generated on that one of the annular collars that facesthe first support, and a stop for the closing body comprising at leastone through-opening for forming a choke for the hydraulic medium extendson that one of the annular collars that faces the second support.
 4. Atappet pushrod of claim 3, wherein the bushing is made as a thin-walledsheet metal part and the annular collar facing the second supportcomprises leaf spring-like tongues between which the through-openingsare formed.
 5. A tappet pushrod of claim 3, wherein the bushing isconfigured as one of a solid or an extruded part, and the annular collarfacing the second support comprises on an inner side, rib-likecircumferential projections between which the through-openings areformed.
 6. A tappet pushrod of claim 2, wherein the tappet pushrodcomprises at least two fabricated sections, a first one of thesesections comprises the first support and a second one of these sectionscomprises the second support, and the two sections are connected by acylindrical part comprising the pipette means and the choke.
 7. A tappetpushrod of claim 6, wherein the cylindrical part is made up of two partsand comprises stub-like extensions pointing away from each other, eachextension being inserted into one of the sections, said extensions arelikewise inserted into each other at inner axial ends and enclose anintermediate closing body, typically a ball, a sealing valve seat forthe closing body for forming the pipette means is configured on an innerend face of one of the extensions and a stop for the closing bodycomprising a choke in the form of at least one through-opening for thehydraulic medium is configured on an inner end face of the other of theextensions.
 8. A tappet pushrod of one of the preceding claims whereinthe supports of the tappet pushrod are configured as ball heads.